Conventionally, as a method for utilization of a semiconductor material functioning as a photocatalyst, it is known to decompose water to produce hydrogen or to generate electrical energy by irradiating a semiconductor material with light (for example, PTL 1).
PTL 1 discloses a photo-assisted water electrolysis apparatus having a function of converting light energy obtained from solar light to hydrogen energy. The photo-assisted water electrolysis apparatus is composed of a plurality of laminated photo-assisted water electrolysis cells. Each photo-assisted water electrolysis cell has a box-like casing whose peripheral portion is surrounded with an outer wall made of a transparent glass or synthetic resin plate, and is arranged in a state of being inclined at a given angle from the horizontal state. An electrolyte is accommodated in a lower portion of the photo-assisted water electrolysis cell, and a separation wall which divides the photo-assisted water electrolysis cell into two spaces is provided in the middle of the thickness direction of the cell. The separation wall is formed by integrally joining a gas separation membrane arranged on an upper side with a photo-assisted water electrolysis electrode/membrane assembly arranged on a lower side, and plays a role of separating the produced hydrogen from the produced oxygen. In the photo-assisted water electrolysis electrode/membrane assembly, a photocatalyst electrode and a platinum counter electrode are respectively formed on both surfaces of a Nafion membrane which is an ionic conductive membrane arranged in the middle of the thickness direction. In the photo-assisted water electrolysis electrode/membrane assembly, irradiation of solar light causes the photo-assisted water electrolysis, and oxygen is produced from the photocatalyst electrode and hydrogen is produced from the platinum counter electrode. Further, the lower end of the separation wall is provided with a rectangular through hole, and the electrolyte can be circulated within the photo-assisted water electrolysis cell through the through hole. Further, in an outer wall of the photo-assisted water electrolysis cell, a rectangular circulation hole in planar view is formed, and a movable wall which makes the opening area of the circulation hole freely variable is provided.
Then, the electrolyte is supplied to each photo-assisted water electrolysis cell by admission through a circulation hole of the electrolyte having overflown from a neighboring photo-assisted water electrolysis cell located on an upstream side. Similarly, the electrolyte is discharged from each photo-assisted water electrolysis cell by effusion of the electrolyte to a neighboring photo-assisted water electrolysis cell located on a downstream side. By employing such a mechanism, a pipe length required for supply/discharge of an electrolyte and the man-hours needed to install piping are reduced.
However, in the case of the above-mentioned photo-assisted water electrolysis apparatus, no contrivance is shown concerning the piping required for collecting the produced hydrogen.
For example, with respect to the photo-assisted water electrolysis apparatus in which a plurality of photo-assisted water electrolysis cells are laminated, a method of attaching separate hydrogen collecting pipes to every photo-assisted water electrolysis cell will be considered. In this method, it is necessary to attach at least the same number of hydrogen collecting pipes as the total number of the photo-assisted water electrolysis cells to be arranged, and further the hydrogen collecting pipes form a plurality of manifolds. In such a configuration, not only the configuration is complicated and the length of hydrogen collecting pipes is significantly long, but also control of circulation of hydrogen is difficult since there are many manifolds, and man-hours required for disposing pipes increase. This is a large problem in considering commercialization of the photo-assisted water electrolysis apparatus.
Then, in view of these conventional problems, it is an object of the present invention to provide a hydrogen producing device which produces hydrogen by utilizing a decomposition reaction of water by an optical semiconductor, and an energy system including the hydrogen producing device. Specifically, the length of a hydrogen collecting pipe connected to each hydrogen producing cell constituting the hydrogen producing device and the number of manifolds are considerably reduced. Further, in order to commercialize the hydrogen producing device, it is essential to produce a sufficient amount of hydrogen by linking a large number of hydrogen producing cells. Accordingly, it is also an object of the present invention to provide a simple and rational member and method for linking the hydrogen producing cells together.